TWI618971B - Photographing apparatus and photographing method - Google Patents

Abstract

A photographing device includes: a light source, irradiating light; a focusing optical system that changes a path of light reflected from an object; a photographing unit that photographs an image of the object formed by the focusing optical system; The adjusting unit adjusts a distance between the focusing optical system and the object. Each time the distance between the focusing optical system and the object changes a specific interval, the imaging unit captures an image of the object, and the specific interval is set to a size smaller than the depth of field of the focusing optical system.

Description

Photographing device and method

The invention relates to a photographing device and a photographing method, and also relates to an auto-focusing technology of a photographing device.

In a laser processing process, it is important to clearly capture the surface of an object. In order to improve the sharpness of an image, it is necessary to perform an operation of changing the focal position of the focusing optical system to an object, and the above-mentioned operation is called an autofocus operation.

The autofocus operation is an operation to find a distance position for achieving a clear image while changing the distance between the focusing optical system and the object. That is, in the auto-focusing process, it is necessary to change the distance between the focusing optical system and the object to perform multiple shooting operations.

However, in order to obtain an image without shaking in a plurality of shooting operations, the image was taken under a static state. However, in this case, a delay time required to wait for the vibration of the device to disappear is consumed, and therefore there is a problem that it is difficult to perform an autofocus operation at high speed. In addition, when an autofocus operation is performed in a moving state, the sharpness of an image is reduced, and therefore there is a disadvantage that it is difficult to find an accurate focus position.

According to the exemplary embodiment, the auto-focus operation of the photographing device can be performed accurately and quickly.

In one aspect, a photographing device is provided, including: a light source that irradiates light; a focusing optical system that changes a path of light reflected from an object; a photographing unit that photographs the object formed by the focusing optical system An image; and a distance adjusting section that adjusts the distance between the focusing optical system and the object; and that the imaging section captures the object whenever the distance between the focusing optical system and the object changes by a specific interval For the image of the object, the specific interval is set to a size smaller than the depth of field of the focusing optical system.

The image capturing unit can capture an image of the object using a global shutter method.

The distance adjusting unit may change the distance between the object and the focusing optical system at a constant speed in at least one section.

The speed at which the distance adjusting unit changes the distance between the object and the focusing optical system may satisfy Equation 1.

(V1 = the magnitude of the speed of the change in the distance between the object and the focusing optical system, f = the number of shots per unit time of the imaging section in the constant speed interval, DoF = the depth of field size of the focusing optical system).

The speed at which the distance adjusting unit changes the distance between the object and the focusing optical system may satisfy Equation 2.

(V1 = the speed of the change in the distance between the object and the focusing optical system, DoF = the depth of field of the focusing optical system, and E = the exposure time per frame of the shooting section)

The exposure time of each frame of the above-mentioned shooting section can satisfy Equation 3,

(E = exposure time per frame of the imaging section, A _pixel = pixel area of the imaging section, M = magnification, V2 _max = maximum value of relative vibration speed between the imaging section and the object).

The imaging device may further include an encoder that senses a change in the distance between the object and the imaging unit to generate an electrical signal.

The imaging device may further include a control unit that generates a synchronization signal to the imaging unit based on the electrical signal generated by the encoder.

The imaging device may further include a processor that receives an image of the object captured by the imaging unit and captures the sharpness of the image.

The processor may determine a distance between the object and the focusing optical system that have captured the image with the highest definition as a focusing distance.

The processor may determine the focus distance by using Equation 4 according to the sharpness value of the image.

(H = distance between the focusing optical system and the object in the focused state, H _i = measured the distance between the focusing optical system and the object at the i-th shooting with the highest resolution, H _i-1 = The distance between the focusing optical system and the object at the i-1th shot, H _{i + 1} = the distance between the focusing optical system and the object at the i + 1th shot, C _i = the highest measured The sharpness value of the i-th captured image, C _i-1 = the sharpness value of the i-1th captured image, C _{i + 1} = the sharpness value of the i + 1th captured image) .

The interval where the distance adjustment unit changes the distance between the object and the focusing optical system can be determined by Equation 5 and Equation 6. H-D-δ <X <H + D + δ ... Equation 5

(X = distance between the support surface of the object and the focusing point of the focusing optical system, H = predicted thickness of the object, D = thickness deviation of the object, δ = acceleration interval, V1 = maximum speed, a = acceleration) .

In another aspect, a photographing method is provided, including the steps of: irradiating light to an object; using a focusing optical system to condense light reflected on the object; adjusting the focusing optical system and the above A step of the distance between the objects; and a step of taking an image of the object each time the distance between the focusing optical system and the object changes by a specific interval; and The specific interval is set to be smaller than the depth of field of the focusing optical system.

In the step of adjusting the distance, the distance between the object and the focusing optical system can be changed at a constant speed in at least one section.

In the step of adjusting the distance, the imaging unit may take an image of the object at a fixed time interval within an interval where the distance between the object and the focusing optical system is changed at a constant speed. The speed at which the distance between the focusing optical systems is changed satisfies Equation 1.

(V1 = the speed of the change in the distance between the object and the focusing optical system, f = the number of shots per unit time of the imaging section in the constant speed interval, DoF = the depth of field of the focusing optical system, α is a value satisfying 0.1 <α <0.5 Arbitrary real number).

In the step of adjusting the distance, the speed of changing the distance between the object and the focusing optical system can satisfy Equation 2.

(V1 = the speed of the change in the distance between the object and the focusing optical system, DoF = the depth of field of the focusing optical system, and E = the exposure time per frame of the shooting section)

The photographing method may further include a step of sensing a change in the distance between the object and the photographing unit to generate an electrical signal.

The photographing method may further include a step of generating a synchronization signal to the photographing unit based on the electric signal.

The photographing method may further include a step of receiving the image of the object captured by the photographing unit and capturing the sharpness of the image.

The above-mentioned shooting method may further include a step of determining a focus distance by using Equation 4 according to the sharpness value of the image,

(H = distance between the focusing optical system and the object in the focused state, H _i = measured the distance between the focusing optical system and the object at the i-th shooting with the highest resolution, H _i-1 = The distance between the focusing optical system and the object at the i-1th shot, H _{i + 1} = the distance between the focusing optical system and the object at the i + 1th shot, C _i = the highest measured The sharpness value of the i-th captured image, C _i-1 = the sharpness value of the i-1th captured image, C _{i + 1} = the sharpness value of the i + 1th captured image) .

According to an embodiment, the imaging device can perform an autofocus operation while the distance between the object and the focusing optical system changes. Therefore, the imaging device can shorten the time required for autofocus.

In addition, the imaging device can obtain a clear image even when the autofocus is dynamically implemented. The shooting device can shoot at least one image captured in the dynamic auto-focusing process within the depth of field range of the focusing optical system.

In addition, the imaging device corrects the accurate focus distance according to the sharpness value of the image, thereby improving the accuracy of the autofocus operation.

1 / f‧‧‧ time interval

10‧‧‧ Object

100, 200, 300‧‧‧ camera

110‧‧‧light source

120‧‧‧ Focusing Optical System

130‧‧‧Distance adjustment section

140‧‧‧Photography Department

160‧‧‧Processor

250‧‧‧ Encoder

355‧‧‧Control Department

C _i ‧‧‧ Determines the sharpness value of the i-th captured image with the highest sharpness

C _{i + 1} ‧‧‧The sharpness value of the _{i +} 1th captured image

C _i-1 ‧‧‧ sharpness value of the _i- 1th captured image

C _max ‧‧‧ maximum resolution

D‧‧‧Thickness deviation of object

H‧‧‧ The distance between the focusing optical system and the object in the focused state

H _i ‧‧‧ the distance measured between the highest resolution focusing optical system and the object to be shot when the i

H _{i + 1} ‧‧‧ The distance between the focusing optical system and the subject during the _{i +} 1th shot

H _i-1 ‧‧‧ The distance between the focusing optical system and the subject at the time of the i-1 shot

H _max ‧‧‧ Gets the height of the image with maximum sharpness

L1‧‧‧ surface

L2‧‧‧Location

P‧‧‧Focus

S1‧‧‧ support surface

S1110 ~ S1160‧‧‧step

t, t0, t1, t2, t3, t ₀ , t ₁ , t ₂ , t _i , t _N , t _i-1 , t _{i + 1} , t _f

V1‧‧‧ The distance between the object and the focusing optical system

δ‧‧‧Acceleration interval

△ h‧‧‧interval

△ t‧‧‧time

FIG. 1 is a diagram showing a photographing device of an exemplary embodiment.

FIG. 2 is a diagram showing a position of a captured image of a shooting unit during auto focusing.

FIG. 3 is a diagram showing a range in which a distance between an object and a focusing optical system is changed by a distance adjusting unit.

FIG. 4 is a diagram exemplarily showing that the moving speed of the focus point changes with time.

FIG. 5 is a diagram showing a photographing apparatus according to another exemplary embodiment.

FIG. 6 is a diagram exemplarily showing an electric signal generated by an encoder.

FIG. 7 is a diagram showing a photographing apparatus according to still another exemplary embodiment.

8 is a diagram exemplarily showing a synchronization signal generated by a control unit.

FIG. 9 is a diagram showing a change in height of a focus point according to time.

FIG. 10 is a graph showing a relationship between the height of a focus point and the sharpness of an image.

FIG. 11 is a diagram showing a processor correcting an autofocus distance.

FIG. 12 is a flowchart showing a photographing method according to an exemplary embodiment.

FIG. 13 is a flowchart illustrating a photographing method according to another exemplary embodiment.

FIG. 14 is a flowchart showing a photographing method according to another exemplary embodiment.

In the following drawings, the same reference numerals denote the same constituent elements. For clarity and convenience of explanation, the dimensions of each constituent element may be exaggerated in the figure. On the other hand, the embodiments described below are merely examples, and various modifications can be implemented based on these embodiments.

The first and second terms can be used to describe various constituent elements, but the constituent elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one constituent element from the other constituent elements.

As long as no other meaning is explicitly mentioned in the text, the singular expression includes Plural expression. In addition, when it is described that a certain part “includes” a certain constituent element, if there is no particularly contrary description, it means that other constituent elements may be further included, and does not mean that other constituent elements are excluded.

In addition, terms such as "... section" and "module" described in the specification refer to a unit that processes at least one function or operation.

FIG. 1 is a diagram showing a photographing apparatus 100 according to an exemplary embodiment.

1, a photographing device 100 according to an exemplary embodiment may include: a light source 110; a focusing optical system 120 that changes a path of light reflected from the object 10; a photographing unit 140 that photographs an object formed by the focusing optical system 120 An image of the object 10; and a distance adjusting unit 130 that adjusts a distance between the focusing optical system 120 and the object 10.

The light source 110 may irradiate light. The light emitted from the light source 110 can be irradiated to the object 10 through a specific optical system. In FIG. 1, an example in which the light emitted from the light source 110 travels as parallel light is shown. However, the embodiment is not limited to this, and an optical system for passing the light emitted from the light source 110 may be differently configured. In addition, the light emitted from the light source 110 may be directly irradiated to the object 10 without passing through the optical system.

The focusing optical system 120 can change the path of the light reflected by the object 10. The light whose path is changed by the focusing optical system 120 may be incident on the image sensor of the imaging unit 140. In FIG. 1, the focusing optical system 120 is shown separately from the photographing unit 140, but the embodiment is not limited thereto. The focusing optical system 120 may also be included inside the imaging section 140. In this case, the distance adjusting unit 130 may change the distance between the focusing optical system 120 and the object 10 by moving the imaging unit 140. The focusing optical system 120 may have a specific focusing distance. Therefore, the surfaces of the focusing optical system 120 and the object 10 are appropriately maintained. At a distance, the imaging unit 140 can obtain a clear image of the object 10.

The object 10 may include a wafer, a semiconductor wafer, and the like as objects to be photographed, and is not limited thereto. The thickness of the object 10 is not constant due to the roughness of the surface. The distance between the surface of the object 10 and the focusing optical system 120 is not fixed according to the flatness of the support surface S1 that supports the object 10. Therefore, in order for the imaging device 100 to obtain an image of the object 10 clearly, the distance between the object 10 and the focusing optical system 120 needs to be appropriately adjusted. A process in which the photographing apparatus 100 adjusts the distance between the focusing optical system 120 and the object 10 in order to obtain an image of the object 10 clearly is referred to as an auto focusing process.

The distance adjusting unit 130 may change the distance between the object 10 and the focusing optical system 120 during the auto-focusing process. The distance adjustment unit 130 is movably mounted on the support surface S1 of the object 10. As another example, the distance adjusting unit 130 can move the focusing optical system 120. When the focusing optical system 120 is built in the photographing section 140, the distance adjusting section 130 may also move the photographing section 140. In addition, the distance adjusting unit 130 can change the distance between the focusing optical system 120 and the object 10 by moving the focusing optical system 120 and the support surface S1 simultaneously.

In order to change the distance between the object 10 and the focusing optical system 120, the distance adjusting unit 130 can move a large-quality moving body including the focusing optical system 120, the imaging unit 140, and the support surface S1. The moving body may refer to a focusing optical system 120, an imaging unit 140, a support surface S1, and the like that are moved by the distance adjustment unit 130 to achieve automatic focusing. During the acceleration / deceleration of the moving body by the distance adjusting unit 130, vibration due to inertial force occurs. For example, when the imaging device 100 images the semiconductor object 10, the imaging unit 140 becomes larger in quality due to the equipment attached to the imaging unit 140, and the mass of the moving body becomes larger. At this time, the distance adjustment unit 130 captures images. When the unit 140 performs acceleration and deceleration, the imaging unit 140 generates vibration due to inertial force.

According to the comparative example, an image of the subject 10 can be captured in a state where the interval between the focusing optical system 120 and the subject 10 does not change. For example, after moving the focusing optical system 120 to a specific position, the image of the object 10 may be captured with the focusing optical system 120 stationary. At this time, in order to obtain a clear image, the photographing unit 140 needs to wait for tens of milliseconds to hundreds of milliseconds until the vibration caused by acceleration / deceleration disappears after the focusing optical system 120 moves and stands still, and then perform image capturing.

For example, when using a lens system with a magnification M and a camera with horizontal and vertical dimensions of px and py, respectively, to shoot at the optimal focus distance, when the vibration velocity vector is set to (vx, vy, vz), Only if vx * E <px / M, vy * E <py * M, and vz * E <DoF are satisfied, a clear image can be obtained. Here, E refers to the exposure time of the imaging unit 140, and DoF refers to the depth of field DoF of the focusing optical system 120, which will be described in detail in the description to be described later.

However, the method of the above comparative example is not conducive to high-speed shooting. In order to find an accurate focus position, the sharpness of an image obtained by changing the distance between the focusing optical system 120 and the object 10 to various distances needs to be compared. However, each time an image is obtained, the vibration due to acceleration and deceleration is reduced, so standby time is required until vx * E <px / M, vy * E <py * M, and vz * E <DoF are satisfied. In addition, the auto-focusing process becomes longer due to the standby time described above. For example, when the mass of a moving body exceeds 30 kg, a standby time of 400 ms or more is required every time an image is captured. Therefore, the delay time required to obtain an image after 10 movements and stillness is 4 seconds or more. This delay time becomes a factor that makes it difficult to achieve high-speed shooting.

According to an exemplary embodiment, in order to achieve faster autofocus, The imaging unit 140 may capture an image of the object 10 while the distance between the focusing optical system 120 and the object 10 changes. That is, while at least one of the object 10 and the focusing optical system 120 moves without being stopped, the imaging unit 140 can capture an image of the object 10. Therefore, there is no need to wait for the vibration caused by acceleration / deceleration to disappear after the moving body is stationary, so the time required for autofocus can be shortened.

The imaging unit 140 can image the object 10 with a global shutter method. Here, the global shutter method refers to a method of obtaining an image by simultaneously exposing all pixels. In contrast, a rolling shutter method is to obtain an image for a line or a group of pixels, and to obtain an image with a time difference for the remaining pixels. If the imaging unit 140 images the object 10 with the global shutter method, a clear image can be obtained even if there is external vibration.

As the distance between the object 10 and the focusing optical system 120 changes, the sharpness of the image captured by the imaging unit 140 changes. When the sharpness of the image captured by the imaging unit 140 is maximized, the distance between the object 10 and the focusing optical system 120 may be referred to as a focal distance. Even if the distance between the object 10 and the focusing optical system 120 does not exactly match the above-mentioned focus distance, the sharpness of the image captured by the imaging section 140 does not change significantly. That is, even if the distance between the object 10 and the focusing optical system 120 is changed in a specific section near the focal distance, the sharpness of the image will not be greatly affected. As described above, an area that maintains the sharpness of an image is referred to as a depth of field (DoF) of the focusing optical system 120.

In the auto-focusing process, the distance between the focusing optical system 120 and the object 10 can be adjusted within the depth of field DoF of the focusing optical system 120. However, if the distance between the imaging unit 140 between the object 10 and the focusing optical system 120 occurs If the image is captured during the change, the image cannot be captured when the focus point is within the depth of field DoF. Therefore, it is not possible to obtain a high-definition image during autofocus, so it may be difficult to find an accurate autofocus position. In order to solve the above-mentioned problem, each time the distance between the focusing optical system 120 and the target object 10 is changed by a specific interval, the imaging unit 140 captures an image of the target object 10. In addition, the specific interval may be set to a size smaller than the depth of field DoF of the focusing optical system 120.

FIG. 2 is a diagram showing the position of a captured image of the imaging unit 140 during autofocus. In FIG. 2, a case where the focusing optical system 120 moves is exemplarily shown, but the embodiment is not limited thereto. For example, the distance between the focusing optical system 120 and the object 10 may be changed by the support surface S1 of the moving object 10.

Referring to FIG. 2, each time the distance between the focusing optical system 120 and the object 10 changes by a specific interval Δh, the imaging unit 140 captures an image of the object 10. In addition, the specific interval Δh may be set to a size smaller than the depth of field DoF of the focusing optical system 120. The above-mentioned specific interval Δh can be fixedly maintained during the auto-focusing process, or it can be changed slightly. However, even if the specific interval Δh is changed, the size may be smaller than the depth of field DoF of the focusing optical system 120. Therefore, even if the shooting is performed halfway between the distance between the subject 10 and the focusing optical system 120, the shooting can be achieved at least once in the depth of field DoF.

In order to increase the working speed of the autofocus, the distance adjustment unit 130 may change the distance between the object 10 and the focusing optical system 120 within a specific range. FIG. 3 is a diagram showing a range in which the distance between the object 10 and the focusing optical system 120 is changed by the distance adjustment unit 130.

Referring to FIG. 3, the distance adjustment unit 130 can move the focus point P of the focus optical system 120 within a specific area. Distance adjustment unit 130 enables focusing optical system The focus point P of 120 moves around the position L2 of the predicted height H of the object 10 from the surface L1 of the support surface S1. For example, the distance adjustment unit 130 can move the focal point P of the focusing optical system 120 while satisfying Equation 1.

[Equation 1] H - D -δ < X < H + D + δ

Here, X = the distance between the support surface of the object and the focal point of the focusing optical system, H = the predicted thickness of the object, D = the thickness deviation of the object, and δ = the acceleration interval.

FIG. 4 is a diagram exemplarily showing that the moving speed of the focus point P changes with time. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the relative speed (moving speed of the focus point P) between the focusing optical system 120 and the object 10.

Referring to FIG. 4, before time t1, the relative speed between the focusing optical system 120 and the object 10 will gradually increase. At this time, the relative speed can be increased with a constant acceleration a. The acceleration interval is an interval in which the distance adjustment unit 130 accelerates at least one of the focusing optical system 120 and the object 10.

As an example, the focus point P of the focusing optical system 120 may move from the surface L1 of the support surface S1 to a height H-D-δ to a height H-D during a time from t0 to t1. The distance δ moved in the acceleration interval can be expressed by Equation 2.

In Equation 2, δ represents the distance traveled during acceleration time, a represents the magnitude of acceleration, and V represents the terminal speed based on acceleration, that is, the maximum speed.

From time t1 to time t2, the focusing optical system 120 and the object 10 The relative speed between them can be kept at a fixed size V1. As an example, during a period from time t1 to time t2, the focus point P of the focusing optical system 120 may move from the surface L1 of the support surface S1 to a height H-D to a height H + D. In addition, from time t2 to time t3, the relative speed between the focusing optical system 120 and the object 10 gradually decreases. At this time, as an example, the relative speed can be gradually reduced with a specific acceleration -a. In addition, during a period from time t2 to time t3, the focus point P of the focusing optical system 120 may move from the surface L1 of the support surface S1 to a height H + D to a height H + D + δ. The distance adjustment unit 130 sets the moving range of the focus point P in consideration of the predicted height H and the thickness deviation D of the object 10, and the speed of finding the focus distance becomes faster and more accurate.

While the focus point P moves from the surface L1 of the support surface S1 to the height H-D to the height H + D, the imaging unit 140 can capture images of the object 10 multiple times. At this time, the focus point P can move at a constant speed, and the magnitude V1 of the moving speed can depend on the exposure time of the imaging unit 140. Here, the exposure time refers to the time during which the imaging unit 140 is exposed to light in order to obtain an image when one shot is taken. The exposure time can be adjusted by the time that the light source 110 irradiates the light. As another example, the exposure time may be adjusted by a shutter or an aperture located inside the imaging section 140.

The moving speed of the focus point P (the magnitude of the change speed of the distance between the object 10 and the focusing optical system 120) V1 can satisfy Equation 3.

In Equation 3, V1 = the magnitude of the change speed of the distance between the object and the focusing optical system, DoF = the depth of field DoF of the shooting section, and E = the exposure time per frame of the shooting section. In addition, as a real number satisfying 0 <α <1, α can be determined by the imaging unit 140 The optical performance varies.

If the focus point P moves too fast, the focus point P will deviate from the depth of field DoF during one frame of the shooting section 140. Therefore, as shown in Equation 3, it is possible to prevent the focus point P from departing from the depth of field DoF at the exposure time required for shooting by limiting the moving speed of the focus point P.

During the auto-focusing process, even if the distance between the focusing optical system 120 and the object 10 is moved at a constant speed, fine vibration occurs in a direction perpendicular to the distance direction between the focusing optical system 120 and the object 10. Therefore, if the exposure time per frame of the imaging unit 140 becomes too long, the sharpness of the image decreases due to the vibration between the focusing optical system 120 and the object 10. In order to prevent the sharpness of the image from decreasing, it is necessary to move the focusing optical system 120 and the object 10 within a 1-pixel range of the imaging unit 140 during each frame exposure time. In order to satisfy the above, the exposure time per frame of the photographing section 140 may satisfy Equation 4.

In Equation 4, E = exposure time per frame of the photographing section 140, A _pixel = pixel area of the photographing section 140, M = magnification, V2 _max = maximum value of the relative vibration speed between the photographing section 140 and the object 10. .

As shown in Equation 4, if the exposure time E of the imaging unit 140 is limited, it is possible to prevent the sharpness of the image from being reduced due to horizontal vibration between the imaging unit 140 and the object 10. For example, when photographing a wafer in a normal wafer grooving process, the field of view (FOV) of the imaging unit 140 needs to be 240 μm × 180 μm to 480 μm × 360 μm, and the optical resolution must be 1.2 μm or less. . When the maximum speed V2 _max of the vibration between the imaging unit 140 and the object 10 is 0.2 mm / s, it is required to be based on Equation 4 in an environment where the pixel size is 4.8 μm × 3.6 μm and the magnification is 10 times. Exposure time within about 2ms. In addition, the output power of the light source 110 required to obtain an image changes according to the exposure time E. For example, the shorter the exposure time E per frame of the photographing unit 140, the greater the light output power required by the light source 110. For example, if the exposure time of the field of view (FOV) of 480 μm × 360 μm is about 2 ms, the minimum output power required by the light source 110 will be about 0.2 W.

While the focus point P is moving from the surface L1 of the support surface S1 to the height H-D to the height H + D at a constant speed V1, the imaging unit 140 can take an image of the object 10 at fixed time intervals. Since the image capturing section 140 captures an image of the object 10 at fixed time intervals, an image can be obtained each time the focus point P moves by a fixed distance. At this time, the moving speed of the focus point P (the relative speed between the object 10 and the focusing optical system 120) V1 and the number of times f of the imaging unit 140 per unit time can satisfy Equation 5.

In Equation 5, V1 = the magnitude of the speed of the change in the distance between the object 10 and the focusing optical system 120, f = the number of shots per unit time of the imaging unit 140 in the constant speed interval, DoF = DoF of the focusing optical system 120 . In addition, α, as a real number satisfying 0 <α <1, can be changed according to the optical performance of the imaging section 140.

Referring to Equation 5, the product of the moving speed V1 of the focus point P and the reciprocal of the number of times f of the imaging unit 140 per unit time may become smaller than the depth of field DoF of the focusing optical system 120. Therefore, even if the imaging is performed while the focus point P is moving, it is possible when the focus point P is in the depth-of-field DoF range of the focusing optical system 120. Take at least one shot. In addition, the focus distance can be derived from a clear image captured in the depth-of-field DoF range.

As an example, in the case of an imaging device used in a general wafer notch, the DoF value may be approximately within 10 μm <DoF <20 μm. In addition, in order to achieve more accurate photography, the above-mentioned value of α * DoF may be required to be approximately within 5 μm. Therefore, V1 / f <5 μm can be satisfied according to Equation 5. As an example, when f = 40Hz, V1 must be satisfied. 0.2mm / s, meets V1 when f = 80Hz 0.4mm / s. The above values are only examples and can be changed depending on the working environment.

When the focus point P is within the depth of field DoF of the focusing optical system 120, a clear image can be obtained. In addition, when the imaging device 100 of the embodiment obtains the clear image, it can be determined that the automatic focusing is achieved. Referring again to FIG. 1, the photographing apparatus 100 may include a processor 160 for evaluating the sharpness of an image photographed by the photographing section 140. The processor 160 may send and receive information to and from the photographing unit 140 through wireless communication or wired communication.

The processor 160 in FIG. 1 may receive image information captured by the imaging unit 140. In addition, the processor 160 may transmit the operation setting information of the imaging unit 140 to the imaging unit 140. The imaging unit 140 may receive operation setting information from the processor 160 to change the operation mode of the imaging unit 140. For example, the processor 160 may transmit the setting information such as the exposure time E, the number of shots per unit time f, and the like to the shooting section 140. In addition, the imaging unit 140 may receive the setting information and change the exposure time E per frame and the number of times of imaging f per unit based on the setting information. In addition, the processor 160 may automatically determine the setting information of the photographing unit 140 according to the above-mentioned expressions 1 to 5. However, the embodiment is not limited thereto. For example, the processor 160 may also be connected through user input. Receives the setting information of the image capturing section 140. To this end, the processor 160 may provide an input interface for inputting setting information. The above input interface can be provided in a button manner or a touch screen manner.

The processor 160 may include an application program (Application Program) for performing the above-mentioned functions, and various databases (DB: Database, hereinafter referred to as "DB") built internally or externally according to circumstances. The DB may be formed inside or outside the processor 160.

As shown in FIG. 3, during a period in which the focus point P moves from the surface L1 of the support surface S1 to the height of H-D to the height of H + D, the photographing unit 140 may transmit the captured images to the processor 160 multiple times. The processor 160 may evaluate the sharpness of an image received from the photographing section 140. For example, the processor 160 may evaluate the sharpness of each image and convert the number of components.

Here, the sharpness of the image may be an evaluation amount determined according to the degree of defocusing when the image is captured. For example, an image captured in a state where the focus point P is out of the depth of field DoF of the focusing optical system 120 is an image captured in a state where the degree of defocusing is severe. In addition, an image captured in a state where the degree of defocusing is severe includes a relatively large portion of blur, so it can be evaluated that the above-mentioned sharpness is low. In contrast, an image captured when the focus point P is located in or near the depth of field DoF is an image captured in a state where the degree of defocusing is relatively low. In addition, since an image captured in a state where the degree of defocusing is low includes less blur, it can be estimated that the sharpness is high.

As an example, the processor 160 may evaluate the sharpness by analyzing the difference between light and dark between the pixels of the image. For example, if there are more blurred parts in the image, the difference between light and dark between pixels will decrease. Therefore, the processor 160 may When the difference between the light and dark of the pixels is not large, it is estimated that the sharpness of the image is low. Conversely, if the image is clear, there will be more sharp changes in the brightness between the pixels. Therefore, the more the area where the amount of light and dark changes between the pixels of the image is larger, the processor 160 may determine that the sharpness of the image is higher.

The processor 160 may determine an image with the highest definition among the images received from the photographing unit 140. In addition, when an image with the highest definition is captured, it can be determined that the distance between the object 10 and the focusing optical system 120 is close to the focusing distance. For example, the processor 160 may receive N images from the photographing unit 140 and evaluate the sharpness of the i-th image as the highest. Therefore, the processor 160 may conclude that the distance between the object 10 and the focusing optical system 120 is closest to the focusing distance when the i-th image is captured.

In order to find an accurate focus position according to the sharpness of the image evaluated by the processor 160, the relative distance between the focusing optical system 120 and the object 10 needs to be known at the time when each image is captured. That is, there is a need for a method in which the position of the focusing optical system 120 and the object 10 can be known each time an image is captured by the imaging unit 140.

FIG. 5 is a diagram showing a photographing apparatus 200 according to another exemplary embodiment.

Referring to FIG. 5, the photographing apparatus 200 according to the exemplary embodiment may further include an encoder 250 that senses a change in the distance between the object 10 and the photographing unit 140 to generate an electrical signal. The remaining constituent elements have been described in the imaging device 100 of FIG. 1, and therefore redundant descriptions are omitted.

The encoder 250 can be linked with the distance adjustment unit 130. The encoder 250 can sense the state of the distance adjustment unit 130 and generate a electric signal based on the state. E.g, Each time the distance adjustment unit 130 changes the distance between the object 10 and the imaging unit 140 by a specific interval, the encoder 250 generates a telecommunication signal. As another example, the encoder 250 may sense the amount of change in the distance between the object 10 and the focusing optical system 120 by itself to generate a pulse signal.

FIG. 6 is a diagram exemplarily showing an electric signal generated by the encoder 250.

Referring to FIG. 6, whenever the distance between the object 10 and the focusing optical system 120 changes by a specific interval, the encoder 250 generates a pulse signal. The frequency of generating the pulse signal may be changed according to the depth of field DoF of the focusing optical system 120. For example, the amount of change in distance between the time when any i-th pulse is generated and the time when the i + 1th pulse is generated may be set to be smaller than the depth of field DoF of the focusing optical system 120 or the same as the size of the depth of field DoF of the focusing optical system 120. Only by setting the distance interval of the pulse signal generated by the encoder 250 to be smaller than the depth of field DoF of the focusing optical system 120, can the position change of the focus point P between adjacent shots be set to be smaller than the depth of field DoF.

In FIG. 6, a pulse signal is shown as an example of an electric signal generated by the encoder 250, but the embodiment is not limited thereto. For example, the encoder 250 may generate different types of electrical signals according to the distance between the object 10 and the focusing optical system 120. In this case, the processor 160 may internally include an algorithm for analyzing the electric signal generated by the encoder 250.

The operation of the imaging unit 140 can be synchronized by a pulse signal from the encoder 250. For example, the imaging unit 140 may count the number of pulses of the pulse signal received from the encoder 250. In addition, each time the number of pulses increases by a specific number, the imaging unit 140 captures an image of the object 10. Moreover, the processor 160 may The number of pulses of the pulse signal received from the encoder 250 is counted. In addition, the processor 160 may know the number of the focusing optical system 120 and the object 10 at the time when the highest-definition image is captured based on the number of pulses counted at the time point when the highest-definition image is received from the imaging unit 140 Distance.

FIG. 7 is a diagram showing a photographing apparatus 300 according to another exemplary embodiment.

Referring to FIG. 7, the photographing apparatus 300 of the embodiment may further include a control unit 355 that generates a synchronization signal to the photographing unit 140 based on the electrical signal generated by the encoder 250. The control unit 355 can receive the electric signal generated by the encoder 250. In addition, the control unit 355 may generate a synchronization signal to the imaging unit 140 based on the electric signal received from the encoder 250. Whenever the distance between the focusing optical system 120 and the object 10 changes by a specific interval, the control unit 355 generates a synchronization signal based on the electric signal provided by the encoder 250. The imaging unit 140 is synchronized by the above-mentioned synchronization signal, so that each time the distance between the focusing optical system 120 and the object 10 changes a specific interval, an image of the object 10 is captured. The specific interval may be set to be smaller than the depth of field DoF of the focusing optical system 120.

In addition, when the processor 160 receives the synchronization signal from the control unit 355 and the image is captured by the imaging unit 140, the processor 160 can know the distance between the object 10 and the focusing optical system 120. In FIG. 7, the processor 160 and the control unit 355 are shown in separate blocks. However, in FIG. 7, only the two configurations are separated according to functions, and the configuration is not limited to the separation of the processor 160 and the control unit 355 in hardware. For example, the processor 160 and the control unit 355 may share the same hardware resource and execute their respective functions. The processor 160 and the control unit 355 may be separated into different devices.

FIG. 8 exemplarily shows a synchronization signal generated by the control unit 355 Illustration. In FIG. 8, the upper graph represents a pulse signal generated by the encoder 250, and the lower graph represents a synchronization signal generated by the control unit 355.

Referring to FIG. 8, each time the number of pulse signals received from the encoder 250 increases by a specific amount, the control unit 355 generates a pulse signal as a synchronization signal. FIG. 8 shows an example in which the control unit 355 generates a pulse signal whenever the number of pulse signals received from the encoder 155 changes in units of three. However, the embodiment is not limited thereto. For example, the number ratio between the pulse signals generated by the control section 355 and the pulse signals generated by the encoder 250 may be smaller than the number shown in FIG. 8, or may be larger than the number shown in FIG. 8.

The control unit 355 can know the interval between the focusing optical system 120 and the object 10 based on the electric signal received from the encoder 250. In addition, the control unit 355 may control the operation mode of the distance adjustment unit 130 based on the interval between the focusing optical system 120 and the object 10.

The control unit 355 can control the distance adjustment unit 130 so that the focus point P moves within a range satisfying Equation 1. At this time, values such as H, D, and δ in Equation 1 may be input through the input of the processor 160 through the face. The processor 160 may transmit the input setting value to the control section 355. The control unit 355 may compare the received setting value with a distance value obtained from the electric signal received from the encoder 250 to determine how the distance adjustment unit 130 operates.

For example, if the control unit 355 receives from the processor 160 the time point HD-δ = 0.64mm, the end point H + D + δ = 0.96mm, and the constant speed V1 = 0.2mm / s in the constant speed motion interval, the control unit 355 can set A control signal is transmitted to the distance adjustment unit 130 so that the height of the focus point P becomes a position of HD-δ = 0.64 mm. In addition, if the height of the focus point P is HD-δ = 0.64 mm, the control unit 355 may transmit a movement end interrupt signal to the processor 160. In addition, if the control unit 355 receives the autofocus start instruction from the processor 160, the control unit 355 may set the height of the focus point P at a position of HD-δ = 0.64mm based on the electric signal received from the encoder 250, with a constant acceleration a (= V1 / △ t) 0.667mm / s ² accelerate from speed 0 to speed V1 0.2mm / s and move at speed V1 0.2mm / s from HD = 0.7mm to H + D = 0.9mm, and then wait The acceleration -a (= -0.667 mm / s ² ) decelerates and stops at a height H + D + δ = 0.96 mm. In addition, the control unit 355 may transmit a movement end interrupt signal to the processor 160. In addition, while the height of the focus point P is changed from the position of HD = 0.7 mm to H + D = 0.9 mm, the control unit 355 may generate pulse signals at intervals of 5 μm. In addition, the imaging unit 140 can image the object 10 by synchronizing the pulse signals. The above numerical values are merely examples, and may be changed according to the embodiment.

FIG. 9 is a diagram showing a change in height of the focus point P according to time.

In FIG. 9, the vertical axis represents the height of the focus point P, and the horizontal axis represents time. For convenience, the state where the autofocus is started is indicated as the origin.

The processor 160 may evaluate the sharpness of the N images received from the photographing section 140. In addition, the processor 160 may determine the ith image with the highest definition among the N images. In addition, the processor 160 may know the height H _{i at} which the i-th shooting is achieved according to a signal received from the control unit 355 or the encoder 250. In addition, the focus point P can be moved to the above-mentioned height H _i .

Referring to FIG. 9, from t ₀ to t ₁ , the focus point P may perform an accelerated movement. As an example, at time t ₀ , the height of the focal point P is 0 in the graph, but it may actually be HD-δ shown in Equation 1. And, at time t ₁ , the height of the focus point P may be HD. The time Δt required for the acceleration movement can be changed according to the magnitude of the constant velocity V1 and the acceleration a.

During the period from time t ₁ to t _N , the focus point P can move at a constant speed. The height of the focal point P can be changed from HD to H + D during a constant-speed motion interval. In a section where the focus point P is moved at a constant speed, each time the focus point P moves by a specific interval Δh, the imaging unit 140 captures an image of the object 10. The specific interval Δh is set to be smaller than the depth of field DoF of the focusing optical system 120, so that at least one shot can be achieved within the depth of field DoF.

In the constant-speed motion interval, shooting is performed at a specific distance interval, so that an image of the object 10 can be captured at a specific time interval 1 / f. The time required for the imaging unit 140 to transmit the image data to the processor 160 may be less than the above-mentioned time interval 1 / f. In FIG. 9, t _i refers to the time when the i-th shooting is achieved in the constant velocity section. In addition, H _i refers to the height of the focus point P when the i-th shooting is achieved in the constant velocity section. After N shots are performed in the constant speed interval, the focus point P can be decelerated. The focus point P may stop at a height H + D + δ.

FIG. 10 is a graph showing the relationship between the height of the focus point P and the sharpness of the image.

Referring to FIG. 10, for clarity in the height C _i H _i i-shot may have the highest value. The processor 160 may determine the height H _i of the image with the maximum definition C _i value among the multiple definition values as the auto-focus distance. The manner in which the processor 160 determines the autofocus distance is not limited to this. For example, processor 160 may further consider the value C of each definition in the adjacent H _i H, H _{i + 1} height _{i-1 i-1, C} i + 1 for correcting autofocus distance.

FIG. 11 is a diagram showing the processor 160 correcting the autofocus distance.

Referring to FIG. 11, the processor 160 may calculate a height H _{max of} an image in which the maximum definition C _max is obtained. As shown in FIG. 11, since the image of the subject 10 is captured discontinuously, the image cannot be captured at the height H _max where the sharpness of the image is the highest. However, in fact, the interval between H _i-1 , H _i , H _{i + 1} is very narrow. Therefore, during the period when the height of the focus point P changes from H _i-1 to H _{i + 1} , the focus can be estimated by a quadratic function. The relationship between the height of the point P and the sharpness of the image. In addition, H _i-1 , H _i , H _{i + 1,} and C _i-1 , C _i , C _{i + 1} can be expressed by Equations 7 to 9 by the approximation method.

Further, the sharpness can be obtained C _max is the maximum height H _max of the image obtained inflection point to a quadratic function as shown in Equation 7 is a formula 9 i.e. -b / 2a. When the height H _max = -b / 2a is obtained from Equation 7 to Equation 9, it can be expressed as Equation 10.

Each processor 160 may calculate the height _{H i-1, H i,} H i + 1 obtained image sharpness _{C i-1, C i,} C i + 1 in accordance with the preferred formula above calculated 10 focusing distance above the height H _max and H _max is determined as the auto-focusing distance. When the processor 160 determines the autofocus distance H _max , the distance adjustment unit 130 can change the distance between the object 10 and the focusing optical system 120 such that the distance between the focus point P and the support surface of the object 10 becomes H _max . .

Hereinabove, the photographing apparatuses 100, 200, and 300 of the exemplary embodiments have been described with reference to FIGS. 1 to 11. Hereinafter, an imaging method using the imaging devices 100, 200, and 300 will be described. All the technical features of the above-mentioned photographing devices 100, 200, and 300 can be applied in the photographing method described below, and repeated description is omitted.

FIG. 12 is a flowchart showing a photographing method according to an exemplary embodiment.

Referring to FIG. 12, the photographing method may include the following steps: step S1110 of irradiating light; step S1120 of condensing light reflected on the object 10 using the focusing optical system 120; adjusting a distance between the focusing optical system 120 and the object 10 Step S1130 of Step 2; and Step S1140 of capturing an image of the object 10 whenever the distance between the focusing optical system 120 and the object 10 changes by a specific interval.

In step S1110, the light source 110 can be used to irradiate the object 10 with light. The light source 110 can adjust the irradiation time of light in a manner corresponding to a specific exposure time E. As another example, the light source 110 may continuously irradiate light, and the aperture of the imaging unit 140 may be operated in accordance with the exposure time E described above. The exposure time E can be determined by Equation 4 in consideration of the pixel size and magnification of the imaging unit 140 and the maximum vibration speed between the focusing optical system 120 and the object 10.

In step S1120, the focusing optical system 120 can be used to focus the light reflected on the object 10. The focusing optical system 120 may have a specific depth of field DoF. The sharpness of an image formed by the light passing through the focusing optical system 120 changes depending on whether the focus point P is located at the aforementioned depth of field.

In step S1130, the relative distance between the focusing optical system 120 and the object 10 can be changed. In step S1130, the distance adjusting unit 130 can focus The moving range of the point P satisfies the above-mentioned expressions 1 and 2.

In step S1140, while the focus point P is moving, the image capturing unit 140 may capture images of the object 10 multiple times. Each time the distance between the focusing optical system 120 and the object 10 changes by a specific interval Δh, the imaging unit 140 captures an image of the object 10. The specific interval Δh may be set to be smaller than the depth of field DoF of the focusing optical system 120. Thereby, even if shooting is performed in an environment where the imaging unit 140 is moving, a clear image can be captured at least once.

FIG. 13 is a flowchart illustrating a photographing method according to another exemplary embodiment.

Referring to FIG. 13, the photographing method may further include a step S1135 of generating a pulse signal according to a change in the distance between the focusing optical system 120 and the object 10. The pulse signal can be generated by the encoder 250 shown in FIG. 5. As another example, the pulse signal may be generated by the control unit 355 of FIG. 7 that has received the electric signal of the encoder 250. The operation of the distance adjusting unit 130 can be controlled based on the pulse signal. In addition, the imaging unit 140 may be synchronized based on the pulse signal.

FIG. 14 is a flowchart showing a photographing method according to another exemplary embodiment.

Referring to FIG. 14, the photographing method may further include the following steps: step S1150 of capturing the sharpness of the image captured by the photographing unit 140; and step S1160 of capturing the focus distance according to the sharpness value of the image.

In step S1150, the processor 160 may receive images from the photographing unit 140 and evaluate the sharpness of each image. In addition, the sharpness of each evaluated image can be converted into a numerical value.

In step S1160, the processor 160 may determine the focus distance according to the sharpness value of the image. As an example, the height H _i that achieves the i-th shooting with the highest definition can be determined as the focus distance. As another example, as shown in FIG. 11, the processor 160 may also calculate the sharpness C _i-1 , C _i , C _{i + 1} of the images obtained at the heights H _i-1 , H _i , H _{i + 1} , respectively. The height H _{max is} determined as the auto-focus distance from the optimal focus distance H _max calculated from the above Equation 10.

In the above, the photographing apparatuses 100, 200, and 300 and the photographing methods using the photographing apparatuses 100, 200, 300 according to the exemplary embodiments have been described with reference to FIGS. 1 to 14. According to the embodiment, the autofocus operation can be performed while the distance between the object 10 and the focusing optical system 120 is changed, thereby reducing the time required for the autofocus. In addition, even if the automatic focusing is dynamically implemented, at least one image is captured within the depth of field range of the focusing optical system 120, thereby obtaining a clear image. In addition, the accurate focus distance is corrected according to the sharpness value of the image, thereby improving the accuracy of the autofocus operation.

In the above description, many matters are specifically described, but these matters do not limit the scope of the present invention and should be interpreted as examples of preferred embodiments. Therefore, the scope of the present invention should not be defined by the illustrated embodiments, but should be defined by the technical ideas recorded in the scope of the patent application.

10‧‧‧ Object

100‧‧‧ shooting device

110‧‧‧light source

120‧‧‧ Focusing Optical System

130‧‧‧Distance adjustment section

140‧‧‧Photography Department

160‧‧‧Processor

D‧‧‧Thickness deviation of object

H‧‧‧ The distance between the focusing optical system and the object in the focused state

P‧‧‧Focus

S1‧‧‧ support surface

Claims (20)

A photographing device includes a light source that irradiates light to an object, a focusing optical system that changes a path of light reflected from the object, and a photographing unit that captures an image of the object formed by the focusing optical system And a distance adjusting section that adjusts a distance between the focusing optical system and the object; and each time the distance between the focusing optical system and the object changes a specific interval, the photographing section Shooting an image of the object, and the shooting unit has a non-zero relative velocity with respect to the object when shooting the image of the object, and the specific interval is set to be smaller than the focusing optical system The size of the depth of field. The photographing apparatus according to item 1 of the scope of patent application, wherein the photographing section photographs an image of the object in a global shutter method. The photographing device according to item 1 of the scope of patent application, wherein the distance adjusting unit changes the distance between the object and the focusing optical system at a constant speed within at least one time interval. The photographing device according to item 3 of the scope of patent application, wherein the speed at which the distance adjusting unit changes the distance between the object and the focusing optical system satisfies Equation 1. V1 = the magnitude of the speed of change in the distance between the object and the focusing optical system, f = the number of shots per unit time of the imaging section in the constant velocity section, DoF = the depth of field size of the focusing optical system. The photographing device according to item 1 of the scope of patent application, wherein the speed at which the distance adjusting unit changes the distance between the object and the focusing optical system satisfies Equation 2. V1 = the speed of the change in the distance between the object and the focusing optical system, DoF = the depth of field of the focusing optical system, and E = the exposure time per frame of the shooting section). The photographing device according to item 1 of the scope of patent application, wherein the exposure time of each frame of the photographing section satisfies Equation 3, E = exposure time per frame of the shooting section, A _pixcl = pixel area of the shooting section, M = magnification, V / 2 _max = the maximum value of the relative vibration speed between the shooting section and the object. The photographing device according to item 1 of the scope of patent application, further comprising an encoder that senses a change in the distance between the object and the photographing unit to generate an electrical signal. The photographing device according to item 7 of the scope of patent application, further comprising a control unit that generates a synchronization signal to the photographing unit based on the electrical signal generated by the encoder. The photographing device according to item 1 of the scope of patent application, further comprising a processor that receives an image of the object captured by the photographing unit and captures the sharpness of the image. The photographing device according to item 9 of the scope of patent application, wherein The processor determines a distance between the object and the focusing optical system that have captured the image with the highest definition as a focusing distance. The photographing device according to item 9 of the scope of patent application, wherein the processor determines the focus distance by using Equation 4 according to the sharpness value of the image, H = distance between the focusing optical system and the object in the focused state, H _i = distance between the focusing optical system and the object at the i-th time when the highest definition is measured, H _i-1 = the The distance between the focusing optical system and the object at the time of the i-1 shot, H _{i + 1} = the distance between the focusing optical system and the object at the time of the i + 1th shot, C _i = the highest sharpness measured The sharpness value of the i-th captured image of the degree, C _i-1 = the sharpness value of the i-1th captured image, C _{i + 1} = the sharpness value of the i + 1th captured image. The imaging device according to item 1 of the scope of patent application, wherein an interval in which the distance adjustment unit changes the distance between the object and the focusing optical system is determined by Equation 5 and Equation 6, HD- δ <X <H + D + δ ... Equation 5 X = distance between the support surface of the object and the focal point of the focusing optical system, H = predicted thickness of the object, D = thickness deviation of the object, δ = acceleration interval, V1 = maximum speed, a = acceleration. A photographing method includes the steps of: irradiating light to an object; and using a focusing optical system to condense light reflected on the object; A step of adjusting the distance between the focusing optical system and the object; and each time the distance between the focusing optical system and the object changes by a specific interval, the photographing section takes a picture of the object The image step, wherein the photographing unit has a non-zero relative speed with respect to the object when taking an image of the object; and the specific interval is set to be smaller than a depth of field of the focusing optical system. The photographing method according to item 13 of the scope of patent application, wherein in the step of adjusting the distance, the distance between the object and the focusing optical system is changed at a constant speed within at least a time interval. The photographing method according to item 14 of the scope of patent application, wherein in the step of adjusting the distance, the photographing unit changes the distance between the object and the focusing optical system at a constant speed within a time interval , Taking an image of the object at a specific time interval, and the speed at which the distance between the object and the focusing optical system is changed satisfies Equation 1, V1 = the speed of the change in the distance between the object and the focusing optical system, f = the number of shots per unit time of the shooting section in the constant speed interval, DoF = the depth of field of the focusing optical system, α is any value that satisfies 0.1 <α <0.5 Real number. The photographing method according to item 14 of the scope of patent application, wherein in the step of adjusting the distance, the speed of changing the distance between the object and the focusing optical system satisfies Equation 2. V1 = the speed of the change in the distance between the object and the focusing optical system, DoF = the depth of field of the focusing optical system, and E = the exposure time per frame of the shooting section. The photographing method according to item 14 of the scope of patent application, further comprising the step of sensing a change in the distance between the object and the photographing unit to generate an electric signal. The photographing method according to item 17 of the scope of patent application, further comprising the step of generating a synchronization signal to the photographing unit based on the electric signal. The photographing method according to item 14 of the scope of patent application, further comprising the step of receiving an image of the object captured by the photographing unit and capturing the sharpness of the image. The photographing method according to item 19 of the scope of patent application, further comprising the step of determining a focus distance by using Equation 4 according to the sharpness value of the image, H = distance between the focusing optical system and the object in the focused state, H _i = distance between the focusing optical system and the object at the i-th time when the highest definition is measured, H _i-1 = the The distance between the focusing optical system and the object at the time of the i-1 shot, H _{i + 1} = the distance between the focusing optical system and the object at the time of the i + 1th shot, C _i = the highest sharpness measured The sharpness value of the i-th captured image of the degree, C _i-1 = the sharpness value of the i-1th captured image, C _{i + 1} = the sharpness value of the i + 1th captured image.